tiffohs, most people put .308 brakes on their 6.5s, but JEC makes a nice brake in a 6.5mm size. its outside diameter is .975 so doesn't match up perfectly, but that's splitting hairs if you ask me. the nice thing about the brake is it is threaded for if you get a suppressor. It is also one of the top performing brakes in many tests. It may not be the very top performing, but then again it doesn't look like a spaceship.
http://shop.jeccustom.com/Quick-Brake-JEC-QB5824.htm